In orthopedic surgery damaged or worn joints can be replaced with prosthesis or implants, such as hip implants, knee implants, etc. The surgery may be planned to select the appropriate type, brand, size, etc. of the implant. This may be made using a technique referred to as templating. Conventionally, this was a manual technique, where pre-printed acetate sheets representing various configurations of implants where overlaid on top of physical x-ray images. Physical x-ray images are two-dimensional representations of a three-dimensional structure. Hence, no depth information is provided during the selection process. Furthermore, x-ray images are associated with magnifications and do not necessarily represent the true geometrical configuration of the patients bone. Thus, this technique can only be a rough guide to select the implant to be implanted. Hence, during the surgery, the surgeon still have to apply care to make sure that the implant selected fits the patient.
U.S. Pat. No. 7,388,972 discloses a templating method using digital x-ray images. In this method a reference object having a known size is scanned together with the patient and thus represented in the x-ray image. Then, the digital X-ray image can be scaled using the reference object. Even if this method may be more accurate than the manual templating technique using physical x-ray images, the scaling is an additional step that takes time and may not be accurate, whereby the selection of implant may be negatively affected. In an embodiment of the method, multiple x-ray images are used for selection of a knee prosthesis, wherein a first image, which is a medio-lateral view, is used for the selection of the femoral component of the implant, and a second image, which is an anterior-posterior view, is used for the selection of the tibial component. However, only one image is used for the selection of each component. Thus, this procedure is also a true two-dimensional planning procedure whereby lack of depth information may lead to the selection of a sub-optimal implant size. For example, an x-ray ray image obtained for a hip surgery is captured perpendicular to the pelvis. However, the femur head, femur neck and femur shaft extend are rotated relative pelvis, i.e. they are not parallel to the pelvis but rather extend from the acetabulum at an angle towards the x-ray image capture system. This has the consequence that true sizes of the femur head, femur neck, and femur shaft are not captured when the image is taken at the same time for the pelvis and femur. Therefore, a 2D image does not capture that the femur is rotated relative to the pelvis, and any templating that rely on such an image will be imprecise.
U.S. Pat. No. 6,002,859 discloses virtual simulation of position and thereby selection of the size of artificial components in three dimensions. Tomographic data is used to generate a three dimensional surface model of the skeletal geometric data. The geometric models of the artificial components can be used in conjunction with the surface model of the skeletal geometric data to determine an initial static estimate of the proper size of the artificial components to be implanted. The size and orientations of the implant component can be fully automated or manually controlled. Manual control is provided in three dimensions simultaneously over the selection of the implant components and the test positions in a biomechanical simulator.
US2010/0153081 discloses planning the position of an implant component relative bone in a coordinate space, such as relative to the base planning coordinate space of a CT volume of the bone. A graphical representation of the bone is in 3D, which can be generated by combining multiple segmented 2D slices, or by a 3D bone model. Multiple restriction axes are displayed for the positioning of the implement component in space. Hence, positioning is made in space and it is made in 3D relative to 3D models of the bone. Therefore, the technique disclosed therein suffers form the issues discussed below with regard to controlling position of virtual components in virtual space. Controlling the positioning in 3D is guided by the restriction axes, which are also provided in 3D space.
US2008/0077003 discloses various disadvantages with planning in 2D coordinates using 2D scan data, and suggests improved techniques by planning in 3D space. Objects, such as models of body parts, are generated and displayed on a monitor in 3D. The objects can be displayed in one or more screen views, i.e. viewing directions to the object. Hence, each screen window comprises a 3D model. The body part is presented in 3D with the object on the screen. The body part is moved and rotated around the virtual object. The respective 3D image data of the object and the body part are not altered during an automatic adaptation, but are visualized. Various three-dimensional representation formats are disclosed. If only 2D data exists for the object, 3D data can be generated from 2D data set based on known symmetries or prior knowledge. The body part is always available in 3D. The techniques disclosed herein are 3D planning, wherein the object as well as the body part are displayed in 3D. In some embodiments, the object is visualized in 2D, but the body part is always displayed in 3D. Hence this technique is a 3D planning technique that suffers form the issues discussed below with regard to controlling position of virtual components in virtual space.
Control of the position of virtual components in three dimensions in virtual space can be difficult for the person performing the pre-operative plan. All three degrees of freedom are manually controlled at the same time when the geometric models of the artificial component are used in conjunction with the surface model of the skeletal geometric data. Therefore, the selected position of the geometric model of the artificial component relative to the surface model of the skeletal geometric data may be imprecise, leading to selection of, e.g., sub-optimal implant. This may also affect any subsequent step that depends on the positioning of the geometric models of the artificial component, such as simulation of movement after selection of component, etc., and ultimately to inferior surgical outcome and patient safety and satisfaction.
Hence, an improved method for planning an orthopedic procedure would be advantageous and in particular allowing for improved precision, increased flexibility, planning efficiency, cost-effectiveness, and/or patient safety would be advantageous.